Method for distributing the total conversion power between the converters of a multiple-converter conversion device

ABSTRACT

A method for distributing the total power of an energy conversion device between at least two converters in the energy conversion device is disclosed. The sum of the conversion powers of the converters is the total power of the conversion device. The energy conversion device converts energy between a first electrical entity and a second electrical entity, where the two converters correspond to at least two portions of a ring, the portions being proportional to a predetermined power value of the respective converters thereof, the combination of the at least two portions forming the whole ring. The total power of the conversion device corresponds to an arc of the ring between the positions of a first slider and a second slider moveable around the ring, and the distribution of power between the converters is determined by the positions of the first and second sliders.

This invention relates to the domain of energy converters and morespecifically conversion devices with multiple converters and thedistribution of power between the different converters.

Typically, a converter supplies a power, known as conversion power, toperform the conversion function. Moreover, a converter draws a power forthe intrinsic operation thereof. The efficiency of a converter isrelated to the ratio between the conversion power and the power drawn bythe converter.

The use of conversion devices with multiple converters in which ahigh-power converter is replaced by a plurality of lower powerconverters operating in parallel supplying an aggregate power equal tothe power supplied by the high-power converter is known in the priorart. Thus, if the conversion power is low, some converters can bedeactivated to save the corresponding power draw thereof.

Furthermore, the efficiency R of a converter as a function of the powerC supplied thereby, as shown in FIG. 1, is not constant. Efficiency islow for low power supplies. It would therefore appear necessary to avoidworking in the low-power zone Z1, in which efficiency is low, andencourage use of the converter in the rated zone Z2 and the high-powerzone Z3, where efficiency is high.

Thus, the use of conversion devices with multiple converters avoids theneed to use a high-power converter in the low-efficiency zone thereofwhen the conversion power thereof is low.

However, the use of multiple-converter conversion devices involves theneed to manage the distribution of the total conversion power betweenthe different converters.

FIG. 2 shows an example trend of a conversion power C as a function oftime t and the corresponding trend of the respective supplied powers ofthe different converters in the case of a conversion device with fourconverters. The powers of the converters are shown by Graphs A, B, C andD. Thus, as the total conversion power increases, the first converter(Graph A) is used up to a first power threshold S1 (corresponding to themaximum power of the first converter), reached at instant t1. Beyond thethreshold S1, the second converter (Graph B) is also used up to a secondthreshold S2 (corresponding to the sum of the maximum powers of thefirst converter and the second converter), reached at instant t2.Equally, the thresholds S3 and S4 are defined by the third and fourthconverters (Graphs C and D). At instant t4, the four converters areused, then the conversion power decreases. The conversion power of thefourth converter is then reduced, then the conversion power of the thirdconverter is reduced, and so on if the conversion power continues todecrease.

Thus, with this power distribution, the first converter (Graph A) isused almost constantly, while the fourth converter (Graph D) is rarelyused. This uneven usage tends to cause a premature wearing of theconversion device due to a premature wearing of the first converter.

The objective of this invention is therefore to disclose a method fordistributing the total conversion power between the converters of amultiple-converter conversion device enabling a near-equal usage of thedifferent converters. The objective of the invention is also to disclosea simple method that does not require complex implementation means.

For this purpose, the invention relates to a method for distributing thetotal power of an energy conversion device between at least twoconverters in said energy conversion device, one converter beingdeactivated when not under load and activated when under load,

-   the sum of the conversion powers of the converters being the total    power of the conversion device,-   the energy conversion device converting energy between a first    electrical entity and a second electrical entity,-   characterised in that:    -   each converter corresponds to a term in a periodic sequence of        period n, n being the number of converters in the conversion        device, and    -   the use of said converters is switched progressively according        to said periodic sequence to balance the conversion power of at        least two converters over time.

According to one embodiment, switching usage of said convertersaccording to said periodic sequence comprises the following steps:

-   -   when the total power of the conversion device increases and the        conversion power of the last of the active converters activated        is greater than or equal to a first predetermined threshold, the        increase is applied to the next converter in the periodic        sequence and,    -   if the total power of the conversion device decreases, the        decrease is applied to the first of the active converters        activated.

According to one embodiment, the first predetermined power threshold isthe maximum power of the converter.

According to one embodiment, if a single converter is active and theaccumulated conversion power of said converter over time sinceactivation thereof reaches a second predetermined threshold, the nextconverter in the periodic sequence is activated.

According to one embodiment, the converters are reversible, and energyconversion may be effected firstly to the second entity and secondly tothe first entity.

According to one embodiment, the first entity is a voltage source andthe second entity is a device used to power an electric motor.

According to one embodiment, the energy conversion device has fourconverters. According to one embodiment, the power of the converters isdistributed as a function of the efficiency characteristics of theconverters.

According to one embodiment, a continuous progressive switching ofconverter activation is commanded according to the periodic sequence.

According to one embodiment, the continuous progressive switching speedis determined as a function of the thermal time constant of theconverters.

According to one embodiment, the continuous progressive switching speedof a first predetermined speed value is increased if the conversionefficiency is less than a first predetermined efficiency value.

According to one embodiment, the continuous progressive switching speedof a second predetermined speed value is reduced if the conversionefficiency is greater than a second predetermined efficiency value.

According to one embodiment, said at least two converters correspond toat least two portions of a ring, the portions being proportional to apredetermined power value of the respective converters thereof, thecombination of the at least two portions forming the whole ring;

-   -   the total power of the conversion device corresponds to an arc        of the ring between the positions of a first slider and a second        slider that are moveable around the ring; and in which    -   the distribution of power between the converters is determined        by the positions of the first slider and the second slider that        are moveable around the ring.

The invention also relates to a method for distributing the total powerof an energy conversion device between at least two converters in saidenergy conversion device,

-   the sum of the conversion powers of the converters being the total    power of the conversion device,-   the energy conversion device converting energy between a first    electrical entity and a second electrical entity,-   characterised in that:

said at least two converters correspond to at least two portions of aring, the portions being proportional to a predetermined power value ofthe respective converters thereof, the combination of the at least twoportions forming the whole ring; and in that

the total power of the conversion device corresponds to an arc of thering between the positions of a first slider and a second slider thatare moveable around the ring, and

the distribution of power between the converters is determined by thepositions of the first slider and the second slider that are moveablearound the ring.

According to one embodiment, the positions of said first and secondmoveable sliders are adjusted such that:

-   -   when the total power of the conversion device increases, the        first moveable slider is moved in a predetermined direction        around the ring proportionally to the power increase and,    -   when the total power of the conversion device drops, the second        moveable slider is moved in a predetermined direction around the        ring proportionally to the power decrease.

According to one embodiment, the positions of the portions of the ringmay be moved in rotation about the centre of the ring, the movement ofthe portions corresponding to a modification of the power distributionbetween the different converters.

According to one embodiment, the movement in rotation of the portions isa function of the efficiency characteristics of the converters.

According to one embodiment, the portions are moved in rotationcontinuously.

According to one embodiment, the speed of movement in rotation of theportions is a function of the thermal time constant of the converters.

According to one embodiment, the speed of movement in rotation of theportions is increased by a first predetermined speed value if theconversion efficiency of the conversion device is less than a firstpredetermined efficiency value.

According to one embodiment, the speed of movement in rotation of theportions is reduced by a second predetermined speed value if theconversion efficiency of the conversion device is greater than a secondpredetermined efficiency value.

The invention also relates to a device for converting energy between afirst electrical entity and a second electrical entity, the energyconversion device comprising at least two converters characterised inthat it also comprises a processing unit configured to implement a powerdistribution method according to the invention.

According to one embodiment, the processing unit includes:

-   -   a module incorporating a representation of a geometric ring,        said at least two converters corresponding to at least two        portions of the ring, the portions being proportional to a        predetermined power value of the respective converters thereof,        the combination of the at least two portions forming the whole        ring;    -   a memory storing the positions of a first slider and a second        slider that are moveable around the ring, the total power of the        conversion device corresponding to an arc of the ring between        the positions of the first and second sliders moveable around        the ring, and    -   a module for distributing the power between the converters        determined by the positions of the first slider and the second        slider that are moveable around the ring.

According to one embodiment, said at least two converters comprise:

-   -   a first input terminal connected firstly to a first extremity of        a branch comprising two switches mounted in series and secondly        to a first output terminal, and    -   a second input terminal connected to the midpoint of the branch        by means of an inductive element, the second extremity of the        branch being a second output terminal,    -   the first input terminals of the converters being connected to        each other, the second input terminals of the converters being        connected to each other, the first output terminals of the        converters being connected to each other, and the second output        terminals of the converters also being connected to each other.

According to one embodiment, the converter switches include a transistormounted in parallel with a diode.

Other characteristics and advantages of the invention are set out in thedescription provided below, with reference to the attached drawings,which show a possible embodiment thereof by way of non-limiting example.

In these drawings, the same reference numbers represent the sameelements:

FIG. 1 is a graph of a characteristic of the efficiency of a converteras a function of the conversion power;

FIG. 2 is a graph of an example trend of a conversion power over timeand the corresponding distribution of the power between the differentconverters of a multiple-converter conversion device;

FIG. 3 is a wiring diagram of a converter;

FIG. 4 is a wiring diagram of a conversion device comprising twoconverters mounted in parallel;

FIG. 5 is a diagram of a power ring according to this invention;

FIG. 6 is a first example of a power trend over time and the applicationof the power ring in FIG. 5 as a function of this trend;

FIG. 7 is a second example of a power trend over time and theapplication of the power ring in FIG. 5 as a function of this trend;

FIG. 8 is a first example of a power transfer in the power ring, asdescribed in FIG. 5;

FIG. 9 is a second example of a power transfer in the power ring, asdescribed in FIG. 5;

FIG. 10 is an example trend of power and temperature of a converter overtime for two different configurations;

The following general definitions apply to the description below:

The term “insulated gate bipolar transistor (IGBT)” is a hybridtransistor, incorporating a metal-oxide semiconductor field effecttransistor (MOSFET) input and a bipolar transistor output.

The term “periodic sequence of period n” refers to a sequence of termsx_(i) such that the ith and the (i+1)th term are identical.

In other words, the term “periodic sequence of period n” corresponds toan “ordered and looped sequence”. The term “ordered and looped sequence”applied to a plurality of elements corresponds to arranging the elementsfrom a first to a last element in a loop, each element appearing onlyonce in the loop, such that the element following the last element isthe first element (and implicitly the element before the first elementis the last element). If there are three elements marked 1, 2 and 3, twoordered closed-loop sequences are possible:

-   -   firstly the sequence corresponding to the loop 1-2-3        (corresponding to the loops 2-3-1 and 3-1-2), and    -   secondly the sequence corresponding to the loop 1-3-2        (corresponding to the loops 3-2-1 and 2-1-3).

The embodiments of this invention relate to the distribution of thetotal conversion power between the converters of a multiple-converterenergy conversion device, i.e. one comprising several converters.

The conversion device enables the energy received in a first form from afirst electrical entity to be converted into a second energy formtransmitted to a second electrical entity. The first electrical entityis for example a voltage source such as accumulation means. The secondelectrical entity is for example a device intended to power an electricmotor to drive a motor vehicle, such as an electrical control circuit ofan electric motor. In this case, the two energy forms are two directvoltages having respectively a first amplitude and a second amplitude.

However, the scope of the embodiments of this invention is not limitedto these examples of electrical entities or to the examples ofconverters described in the description below. The invention applies toall energy converters linking two electrical entities.

FIG. 3 shows an example converter 1 comprising:

-   -   a first input terminal 3 connected firstly to a first extremity        5 of a branch 7 comprising two switches 9 mounted in series and        secondly to a first output terminal 11, and    -   a second input terminal 13 connected to the midpoint 15 of the        branch 7 (corresponding to a point located between the two        switches 9) by means of an inductive element 17, the second        extremity 19 of the branch being connected to a second output        terminal 21.

The switches 9 comprise a transistor 23, usually an IGBT, mounted inparallel with a diode 25, which creates a reversible converter. Thus,conversion can be effected from the input terminals 3 and 13 to theoutput terminals 11 and 21 and vice versa. If conversion is effectedfrom the input terminals 3 and 13 to the output terminals 11 and 21, theconverter is a step-up circuit. If conversion is effected from theoutput terminals 11 and 21 to the input terminals 3 and 13, theconverter is a step-down circuit.

FIG. 4 shows a conversion device 27 comprising two converters asdescribed in FIG. 3 mounted in parallel. Paralleling involvesconnecting:

-   -   the first input terminals 3 to each other,    -   the second input terminals 13 to each other,    -   the first output terminals 11 to each other, and    -   the second output terminals 21 to each other.

The conversion device 27 therefore comprises two output terminals 11 and21 and two input terminals 3 and 13 as is the case with a singleconverter.

By connecting the input and output terminals of the converters 1 in thesame fashion, any number of converters 1 may be paralleled. Theconverters 1 therefore form a conversion device 27. The total power ofthe conversion device 27 is the sum of the conversion powers of theconverters 1. Thus, a large number of low-power converters 1, i.e.converters that can transmit a low power, can replace one high-powerconverter, i.e. a converter that can transmit a high power.

Paralleling the converters 1 makes it possible to use certain converters1 while the others are deactivated. For example, in the case of lowtotal conversion power, some converters 1 can be deactivated in order tosave energy and therefore to optimise the overall efficiency of theconversion device 27. Thus, if a converter is no longer under load (i.e.the conversion power thereof is zero), it is deactivated such that itdraws no power.

In the case of converters 1 as described in FIG. 4, this deactivationmay be effected by leaving the switches 9 of the corresponding converter1 open.

Furthermore, in order to prevent an imbalance in the use of theconverters over time and to enable an even wearing of the differentconverters, the embodiments of this invention describe the application,by a processing unit, of a “rotation” or switching related to the use ofthe different converters.

In order to apply this rotation, each converter 1 corresponds to a termin a periodic sequence of period n. The period n of the periodicsequence is the number of converters 1 in the conversion device 27.

Thus, the use of the converters is switched progressively according tothe periodic sequence. This makes it possible to balance the conversionpower of the converters 1 over time.

During the first use of the conversion device (or on each activation ofthe conversion device), an initialisation process selects, in apredetermined or random manner, a converter to be active. The converterselected begins to supply the power of the conversion device 27.

Once the initialisation process is complete and one of the converters isactivated, according to one embodiment of this invention, the power isthen distributed as follows.

When the total power of the conversion device 27 increases, the increaseis applied to the last of the active converters 1 activated. In otherwords, the conversion power of the last converter 1 activated increasesin line with the increase in the total power of the conversion device27.

When the total power of the conversion device 27 increases and theconversion power of the last of the active converters I activatedreaches a first predetermined threshold, the increase in the total powerof the conversion device 27 is applied to the next converter 1 in theperiodic sequence. If it is inactive, the next converter 1 in theperiodic sequence is activated.

For example, the values of the first predetermined thresholds aredefined such as to optimise the efficiency of the converters.

For example, the first predetermined threshold of a converter 1 is themaximum power level that can be supplied by the converter. Thus, theconversion device 27 provides a maximum power when all of the converters1 are activated at a power level equal to the respective predeterminedthresholds thereof.

If the total power of the conversion device 27 decreases, the decreaseis applied to the first of the active converters 1 activated.

If the first of the active converters activated is no longer under load(i.e. the conversion power thereof is zero), it is deactivated. When aconverter is deactivated, the power drawn by that converter is zero.Thus, the power drawn by the conversion device 27 is reduced. The nextconverter in the periodic sequence then becomes the first of the activeconverters activated. Subsequent power reductions are then applied tothis converter.

Furthermore, according to one embodiment, in order to avoid always usingthe same converter during a duty cycle of the conversion device in whichthe power variations are low for a long period of time, a totalconversion power over time since activation thereof, i.e. the energysupplied by the converter from the time it is activated, can bedetermined. Thus, if a single converter is active and the accumulatedconversion power of this converter over time, since activation thereof,reaches a second predetermined threshold, the next converter in theperiodic sequence is activated. Thus, in the event of an increase of thetotal conversion power of the device, this power is added to theconversion power of the newly activated converter (in the event of areduction of the total conversion power of the conversion device, thispower reduction is applied to the conversion power of the first of theactive converters activated).

This second predetermined threshold is, for example, determined on thebasis of the thermal time constant of the converter. This prevents theconverter 1 from overheating.

The distribution of power may be represented simply using a geometricring referred to below as the power ring. A representation of such aring 29 is provided in FIG. 5 in the case of four converters of the samepower mounted in parallel. The different converters correspond to aportion of the ring 29. Taken together, the portions make up the entirering 29. The portions are proportional to the first power threshold ofthe respective converters. In the example given in FIG. 5, the fourconverters 1 have the same first predetermined threshold value, suchthat the different proportions are the same size. In a specific example,the first threshold is the maximum power level that can be supplied by aconverter.

If, for example, each converter has a power of 10 kW, one quarter ringis equivalent to 10 kW and the entire ring corresponds to 40 kW. Thus,if the power amounts to 15 kW, only two converters are required and theother two may be deactivated.

In FIG. 5, the power ring 29 is divided into four portions, delimited bya vertical axis Δ and a horizontal axis β. The portions are quarterrings marked respectively C1, C2, C3 and C4. In the remainder of thedescription, the corresponding converters shall also be referred to asC1, C2, C3 and C4.

Moreover, the ring 29 has a first slider 31 and a second slider 33 thatare movable around the ring 29 and that define the distribution of powerbetween the four converters. The total power of the conversion device 27corresponds to an arc 100 of the ring 29 between the positions of thefirst slider 31 and the second slider 33 that are moveable around thering 29.

Thus, the positions of the first movable slider 31 and the secondmovable slider 33 are determined such that when the total power of theconversion device 27 increases, the first moveable slider 31 is moved ina predetermined direction around the ring 29, proportionally to thepower increase.

If the total power of the conversion device 27 drops, the secondmoveable slider 33 is moved in the same predetermined direction aroundthe ring 29 proportionally to the power decrease.

Thus, the positions of the sliders 31, 33 define the power distributionof the converters 1 of the conversion device 27.

For example, the predetermined direction is clockwise. In order tobetter explain the operation of the power ring 29, an example trend ofthe distribution of power over time is described in relation to FIG. 6.

FIG. 6 comprises two parts a), b). The top part a) shows the trend ofthe total power of the conversion device 27 as a function of time t. Thebottom part b) shows the trend of the corresponding positions of thefirst slider 31 and the second slider 33 around the ring 29.

Initially, the two sliders 31 and 33 are positioned in the same place onthe ring 29, at an intermediate point between two portions of the ring29. For example, the two sliders 31 and 33 are positioned at point P0 ifthe converter C1 has been selected during the initialisation process.

Immediately after the instant t0, the total power of the device 27increases up to a first power level L1, the first slider 31 then movesaround the ring 29 by a distance proportional to the first power levelL1 to reach position P1. The route of the first slider 31 is entirelywithin the portion of the converter C1. The power increase is thereforeborne solely by the first converter C1 such that only this firstconverter is active. As the power is constant between instants t0 andt1, the first slider 31 remains in position Pl.

Immediately after instant t1, the total power of the device 27 increasesup to a second power level L2. The first slider 31 is moved around thering 29 by a distance proportional to the power increase L2-L1 of thedevice 27. The first slider 31 reaches position P2, which is in theportion corresponding to the converter C2. The power increase L2-L1 ofthe device 27 is therefore borne by the first converter C1 then by thesecond converter C2. Thus, at instant t2, both converters C1, C2 areactive.

Immediately after instant t2, the power level of the device 27 drops tolevel L3. The second slider 33 is moved around the ring 29 by a distanceproportional to the power drop L2-L3. The second slider 33 is moved fromposition P0 to position P3. Positions P0 and P3 are on the portioncorresponding to converter C1. The power drop is then applied to thefirst converter C1 (which is the first of the active convertersactivated). Thus, at instant t3, both converters C1, C2 are active.

Immediately after instant t3, the power level of the device 27 returnsto level L2. The first slider 31 is moved around the ring 29 by adistance proportional to the power increase L2-L3. The first slider 31is moved from position P3 to position P4, which is in the portioncorresponding to converter C3. The power increase L2-L3 of the device 27is therefore borne by the second converter C2 then by the thirdconverter C3. Thus, at instant t4, all three converters C1, C2, C3 areactive.

Immediately after instant t4, the power level drops to a level L4. Thesecond slider 33 is moved around the ring 29 by a distance proportionalto the power drop L2-L4. The second slider 33 is moved from position P3to position P5, which is in the portion corresponding to the converterC3. Thus, at instant t5, the first converter C1 and the second converterC2 are inactive; only converter C3 is active.

Consequently, application of such an embodiment makes it possible todistribute the total conversion power throughout all of the convertersduring the power increase and decrease cycles, even if the instantaneoustotal conversion power is low.

Moreover, as described above, the conversion device 27 is reversible andcan therefore work in both directions, from a first electrical entity toa second electrical entity or from the second electrical entity to thefirst electrical entity.

Assuming again that the electrical entities connected to the conversiondevice are respectively accumulation means and an electrical controlcircuit of an electric motor intended to drive a motor vehicle, thefirst conversion direction corresponds to powering the motor usingaccumulation means while the opposing direction corresponds toregenerative braking enabling the accumulation means to be recharged.The power is then distributed between the different converters in thesame manner for both directions of power transfer.

Power conversion in the opposing direction can be considered to be a“negative” power. In other words, a negative power corresponds to apower transfer from the second electrical entity to the first electricalentity. However, the movements of the first slider 31 and the secondslider 33 are exactly as described above.

Thus, on the power ring 29:

-   -   if the “negative” power increases by an absolute value, i.e. the        total power of the conversion device becomes increasingly        negative, the second slider 33 moves in the predetermined        direction, and    -   if the “negative” power drops by an absolute value, i.e. the        total power of the conversion device becomes decreasingly        negative, the first slider 31 moves in the predetermined        direction.

This can be better understood with reference to FIG. 7. FIG. 7corresponds to FIG. 6, in which a conversion cycle corresponding to theperiod of time between t5 and t6 has been added. This cycle correspondsto a cycle in which the total power of the conversion device 27 isnegative and corresponds to a level L5.

At instant t5, the power drops to zero. On the ring 29, this correspondsto an overlapping (not shown) of the positions of the first slider 31and the second slider 33.

The total power of the conversion device 27 then becomes negative,indicating that the power is being transferred from the second entity tothe first entity. The total conversion power drops to a level L5. Thesecond slider 33 then moves from position P5 to position P6. Thus, thesecond slider 33 is “in front of” the first slider 31, the portionlocated “between” the two sliders 33 and 31 corresponding to the“negative” power.

Thus, use of the two sliders 31 and 33 makes it possible to manage powerdistribution in both directions of conversion.

However, when applying the power distribution described in the aboveembodiments, some converters 1 may be used in their low-power zone suchthat the overall efficiency is not optimum and may be further optimised.

Returning to FIG. 2, the conversion powers marked with the referencesign 2 correspond to a low efficiency of the converter 1, as describedin zone Z1 in FIG. 1.

In order to avoid such a situation, according to one embodiment of thisinvention and as a function of the efficiency characteristics of theconverters 1, the total power of the conversion device 27 is distributedsuch as to optimise the conversion efficiency between the converters 1.

Thus, in particular if the power is constant, if several converters 1are activated, a progressive switching (or power transfer) between thelast converter 1 activated and the first active converter 1 activated isapplied in order to obtain a power distribution corresponding to anoptimised conversion efficiency of the conversion device 27.

Indeed, on the basis of efficiency as a function of conversion power fora converter 1 (as described in FIG. 1), an optimum power distribution asa function of power may be calculated or determined for a conversiondevice 27 comprising a set of converters 1.

Nonetheless, in order to simplify implementation of such a distributionand on account of the fact that a converter used at the maximumconversion power thereof is efficient, this embodiment involvesoptimising the distribution of the partially used converters 1, i.e. theconverter 1 activated last and the first of the active converters 1activated (the other converters being used at full power or beinginactive).

On the power ring 29, such a power distribution is shown by a rotationalmovement of the portions of the power ring 29.

FIG. 8 shows three configurations of the power ring 29, previouslydescribed in FIG. 5, corresponding to three stages or instants ofimplementation of such an optimisation.

The first part a) of FIG. 8 shows an example of power distribution inwhich a first converter C1 is used at full power and a second converterC2 is used at low power (which corresponds to a low efficiency of theconverter C2). The power of the conversion device 27 remains constantover time.

Power is transferred from the first converter C1 to the second converterC2. The transfer is represented on the ring 29 by a rotation of theportions about the centre of the ring 29.

Part b) of FIG. 8 shows an intermediate stage of such a power transfer.It should also be noted that power can also be transferred to theconverter C4. In this case, the portions are rotated in the oppositedirection. The portions are rotated to obtain a power distributioncorresponding to an optimised efficiency. The optimised efficiency may,for example, be determined on the basis of a characteristic representingthe efficiency of the converter 1 as a function of conversion power, andestablished by the manufacturer of the conversion device 27 and recordedin a memory of the conversion device 27.

Thus, in this example, the optimum distribution (corresponding to anoptimised efficiency of the conversion device 27) corresponds to anequal distribution of the total power of the conversion device 27between the two converters C1 and C2 as shown by the position of theaxes on part c) of FIG. 8.

Furthermore, in the case of total power of the conversion device 27remaining constant for a long period of time, the same converters 1 areused throughout this long period of time, which may in particular causethe overheating, and therefore premature wearing, thereof. In order toavoid such overheating, according to one embodiment of this invention, acontinuous progressive switching of activation of the converters 1 iscommanded according to the periodic sequence, such that:

-   -   if only one converter is activated, power is transferred from        the active converter to the next converter in the periodic        sequence (applying this condition, a second converter is active        such that the following example then applies).    -   if several converters are activated, power is transferred from        the first of the active converters activated to the last        converter activated.

Application of this embodiment therefore enables the conversion power tobe transferred continuously and successively to all of the converters 1.This transfer may be effected when the total power of the conversiondevice 27 is constant, or continuously, regardless of the trend of thetotal power of the conversion device 27.

Furthermore, it should also be noted that power can also be transferredto the previous converters.

On the power ring 29, the power transfer is represented by a continuousmovement in rotation of the portions of the ring 29 (the direction ofrotation then defining the direction of transfer (to the previousconverters or to the next converters in the periodic sequence)).

However, according to one alternative embodiment, this movement inrotation of the portions of the ring 29 may be effected periodically,the amplitude and the rotation period being then predefined as afunction of the characteristics and in particular the thermal timeconstant of the converters.

FIG. 9 shows the trend in the power distribution over time at fivedifferent instants during application of this embodiment. In the examplein FIG. 9, the total power of the connection device 27 remains constantfor five instants and the power is transferred to the previousconverters 1 in the periodic sequence. At a first instant (part a)), thetotal power of the conversion device 27 is fully distributed to thefirst converter C1. At a second instant (part b)), one part of the powerhas been transferred from the first converter C1 to the fourth converterC4. At a third instant (part c)), the power is equally distributedbetween the first converter C1 and the fourth converter C4. At a fourthinstant (part d)), the power is fully distributed to the fourthconverter C4. At a fifth instant (part e)), one part of the power hasbeen transferred from the fourth converter C4 to the third converter C3.

The power is therefore transferred continuously from one converter 1 tothe next converter in the periodic sequence such as to obtain anear-equal use of the converters 1 over time.

Thus, applying a continuous rotation of the portions (corresponding to acontinuous transfer to the previous (or next) converters), alsodistributes power to all of the converters over time, regardless of thepower trend.

A continuous progressive switching (or transfer) of power from oneconverter 1 to the next converter has just been described, but the speedof this switching has not been discussed.

According to one embodiment of this invention, the switching speed isdetermined as a function of the thermal time constant of the converters1 such as to limit overheating of the converters 1.

FIG. 10 shows a sample trend of the conversion power C and temperature Tof a converter 1 over time t in the case of intensive usage (part a) andin the case of intermittent usage (part b).

In the case of intensive usage (part a), which often occurs with a powerdistribution according to the prior art as described in FIG. 2, theconversion power is constant and corresponds to the maximum power of theconverter 1. The temperature increases progressively from the instant t0before reaching a temperature plateau Tm at instant t3. The temperatureTm corresponding to this plateau is high, which may be harmful tooperation of the conversion device 27.

In the case of intermittent usage (part b), which occurs when applyingcontinuous switching as described above, when the conversion device 27is not being used at full power, the power increases progressively fromt0 before reaching a plateau at instant t2 corresponding to the maximumconversion power of the converter 1. The plateau extends until instantt2. The power then drops progressively, the cycle is repeated once allof the converters 1 have been used during the switching (or “rotation”)according to the periodic sequence.

In this case, the temperature increases progressively, but more slowlythan in part a) because the power is lower, between t0 and t1, then itcontinues to increase until t2 before reaching a maximum temperature Tnat instant t2, then it again drops progressively as the power decreases.The temperature Tn obtained is less than the temperature Tm because fullpower is only applied for a limited time, which helps to preventexcessive overheating of the converters 1.

As the temperature trend of the converter 1 over time as a function ofconversion power is dependent on the thermal time constant of theconverter 1, the transfer speed is then determined in relation to thistime constant to limit overheating in an optimised manner. On the powerring 29, the switching speed (or transfer speed) is represented by thespeed of movement in rotation of the portions about the centre of thering 29.

Furthermore, the transfer speed may be uniform, but may also bemodulated as a function of a parameter in order to improve the overallefficiency of the conversion device 27. As described previously in FIG.8, some power distributions correspond to an efficiency of theconversion device 27 that is not optimised, while some powerdistributions correspond to an optimised efficiency of the conversiondevice 27. During application of a continuous switching, there is asuccession of configurations corresponding to non-optimised efficienciesthen optimised efficiencies. In order to improve the efficiency of thedevice 27, according to one embodiment of this invention, the powertransfer speed is therefore modulated such that:

-   -   the continuous progressive switching speed of a first        predetermined speed value is increased if the conversion        efficiency is less than a first predetermined efficiency value,        and    -   the continuous progressive switching speed of a second        predetermined speed value is reduced if the conversion        efficiency is greater than a second predetermined efficiency        value.

The first and second predetermined speed values are established as afunction of the characteristics of the converters 1 and in particularthe thermal time constant thereof. The first and second predeterminedefficiency values are established as a function of a characteristicrepresenting the efficiency of the converters 1 as a function of theconversion power.

The first and second efficiency values may be the same. The same is truefor the first and second predetermined speed values.

This modulation amounts to reducing the time spent on the powerdistribution configurations for which efficiency is not optimised andincreasing the time spent on the power distribution configurations forwhich efficiency is optimised.

On the power ring 29, the variation in the switching speed isrepresented by the variation in the speed of rotation of the portionsaround the ring 29.

Thus, by applying a progressive switching to the conversion device 27comprising a plurality of converters mounted in parallel, theembodiments of this invention enable the use of all of the converters ofthe device in a near-equal manner over time, regardless of the totalconversion power of the conversion device 27. Furthermore, byimplementing continuous power switching between the converters 1, theembodiments of this invention enable overheating in the converters 1 tobe limited.

Finally, the use of a power ring 29 enables distribution of powerbetween the converters 1 to be managed simply, according to theembodiments of this invention.

Indeed, it is not necessary to store in real time the usage times orrespective power draws of the converters 1 to equalise the service livesthereof or distribute the power between them. If the total conversionpower varies, the movements of the first slider 31 and the second slider33 ensure that, statistically over a usage period of the conversiondevice 27, the converters 1 are used for approximately identical periodsof time. This is also true if the instantaneous total conversion poweris less than the power supplied by one converter 1.

The method also enables the distribution of power between the converters1 to be optimised while supplying a continuous conversion power. Indeed,in the methods in the prior art, if the total conversion power is belowa threshold, one or more converters are deactivated and the output ofthe other converters is increased in order to improve the overallefficiency of the device, with the same total conversion power. Thisresults in a discontinuity in the total conversion power, at leastduring the transition phase. Managing power distribution through thepositions of the first slider 31 and the second slider 33 on the ring 29ensure that the output signal from each converter 1 is decreased andincreased progressively. The converters 1 of the conversion device 27are not deactivated abruptly.

Furthermore, the rotation of the portions of the ring 29 (or,equivalently, the axes Δ, β separating the portions) help to improvepower distribution and equalise use of the converters 1 if the totalconversion power is constant. The rotation of the portions of the ring29 also provides a continuity of the total conversion power if thislatter is constant and use of the converters 1 is to be alternated.

The energy conversion device 27 may include a processing unit configuredto implement the method according to the invention.

For example, the processing unit includes a module incorporating arepresentation of the geometric ring 29. In particular, the ring 29 maybe stored in a memory in the form of several angular intervals eachcorresponding to a respective converter 1. The positions of the firstslider 31 and the second slider 33 may correspond to respective angularvalues stored in a memory.

Furthermore, the distribution of power between the converters 1 may berepresented by the ring 29 on a display unit in order to keep a user ofthe energy conversion device 27 informed.

The invention claimed is:
 1. A method for distributing a total power ofan energy conversion device between at least two converters in saidenergy conversion device, a sum of the conversion powers of theconverters being the total power of the energy conversion device, themethod comprising: converting, by the energy conversion device, energybetween a first electrical entity and a second electrical entity,wherein: said at least two converters correspond to at least twoportions of a ring, said ring being stored in a memory in a plurality ofangular intervals, each corresponding to a respective converter, the atleast two portions being proportional to a predetermined power value ofthe respective converters thereof, a combination of the at least twoportions forming an entirety of the ring; and the total power of theenergy conversion device corresponds to an arc of the ring betweenpositions of a first moveable slider and a second moveable slider thatare moveable around the ring said positions of the first slider and thesecond slider corresponding to respective angular values stored in thememory; and determining the distribution of power between the convertersby positions of the first slider and the second slider that are moveablearound the ring.
 2. The method according to claim 1, wherein thepositions of said first moveable slider and said second moveable sliderare adjusted such that: when the total power of the energy conversiondevice increases, the first moveable slider is moved in a predetermineddirection around the ring proportionally to the power increase and, whenthe total power of the energy conversion device drops, the secondmoveable slider is moved in a predetermined direction around the ringproportionally to the power decrease.
 3. The method according to claim 1wherein positions of the at least two portions of the ring may be movedin rotation about a centre of the ring, the movement of the at least twoportions corresponding to a modification of the power distributionbetween the different converters.
 4. The method according to claim 3,wherein the at least two portions are moved in rotation continuously. 5.The method according to claim 3, wherein the movement in rotation of theat least two portions is a function of efficiency characteristics of theat least two converters.
 6. The method according to claim 3, wherein aspeed of movement in rotation of the at least two portions is a functionof the thermal time constant of the at least two converters.
 7. Themethod according to claim 3, wherein a speed of movement in rotation ofthe at least two portions is increased by a first predetermined speedvalue when a conversion efficiency of the energy conversion device isless than a first predetermined efficiency value.
 8. The methodaccording to claim 3, wherein a speed of movement in rotation of the atleast two portions is reduced by a second predetermined speed value ifthe conversion efficiency of the energy conversion device is greaterthan a second predetermined efficiency value.
 9. An energy conversiondevice for converting energy between a first electrical entity and asecond electrical entity, the energy conversion device comprising: atleast two converters; a processing unit configured to implement a powerdistribution method, the processing unit comprising: a moduleincorporating a representation of a geometric ring, said ring beingstored in a memory in a plurality of angular intervals eachcorresponding to a respective converter, said at least two converterscorresponding to at least two portions of the ring, the at least twoportions being proportional to a predetermined power value of therespective converters thereof, the combination of the at least twoportions forming the ring in its entirety; the memory for storingpositions of a first slider and a second slider, the first and secondsliders being moveable around the ring, said positions of the firstslider and the second slider corresponding to respective angular valuesstored in the memory, the total power of the energy conversion devicecorresponding to an arc of the ring between the positions of the firstslider and the second slider that are moveable around the ring, and amodule for distributing the power between the at least two convertersdetermined by the positions of the first slider and the second sliderthat are moveable around the geometric ring.
 10. The device according toclaim 9, in which said at least two converters comprise: a first inputterminal connected firstly to a first extremity of a branch comprisingtwo switches mounted in series and secondly to a first output terminal,and a second input terminal connected to a midpoint of the branch by aninductive element, a second extremity of the branch being a secondoutput terminal, the first input terminals of the converters beingconnected to each other, the second input terminals of the at least twoconverters being connected to each other, the first output terminals ofthe at least two converters being connected to each other, and thesecond output terminals of the at least two converters also beingconnected to each other.
 11. The device according to claim 10, in whichthe switches of the at least two converters include a transistor mountedin parallel with a diode.